This invention relates to a method of shaping the distal surface of a human femur using certain alignment guides to guide the shaping of that surface to receive a distal femoral prosthesis and to certain apparatus used in the method.
Various types of alignment guides and methods have been developed to enable a surgeon to affix a distal femoral knee prosthesis to the human femur. Since the purpose for affixing such a prosthesis is to restore the patient's ability to walk after disease or other traumatic causes have impaired that ability, it is important that the prosthesis be attached to the femur in such a manner that it will approximate as closely as possible the natural condyles which the prosthesis is replacing. If the prosthesis is not properly affixed with respect to the femur, an unnatural gait or other complications can result.
It is common practice to use the long central axis of the femur as a guide in determining the manner in which the distal femoral surface should be shaped to receive a properly aligned distal femoral prosthesis. Generally, a pre-operative single, long anterior-posterior radiograph showing the shaft of the tibia and femur is made and the angle of the long central axis of the femur relative to the vertical axis of the body (physiological valgus, generally from 5.degree.-12.degree.) is visualized. That angle is then used as a reference when the distal femoral surface is shaped using various cutting instruments and guides. In one such method, a long axial alignment jig (rod) is employed which is positioned over the outside surface of the patient's leg in a position which the surgeon visually determines to correspond to the central long axis of the femur and the femur is shaped relative to the alignment of that rod. One example of the manner in which the distal femoral surface is shaped to receive a prosthesis using an external alignment rod is shown in "The HOWMEDICA Universal Total Knee Instrument System", brochure no. H-2026 -1 1/82 15M B (1980) from HOWMEDICA, Inc., Orthopaedics Division, Rutherford, NJ 07070 which is hereby incorporated by reference.
The external alignment rod has a disadvantage in that the surgeon is relying upon visual and tactile means for positioning the alignment rod and thereby the femoral surface resection guide since the patient's skin covers the major portion of the femur and screens it from view.
One part of the method described in the aforementioned Howmedica, Inc., brochure employs the use of a femoral drill jig having two posterior skids which align with the posterior surfaces of the femoral condyles and a drill bit which is caused to rest in the center of the patello-femoral (intercondylar) groove to obtain correct medial-lateral and rotational positioning of the jig prior to using the jig to bore holes in the femur to receive the fixation studs of a distal femoral prosthesis. Thus, reference points located directly on the distal femoral surface are employed to position the jig. However, the initial reaction of the distal femoral condyles is made using a jig employing an external alignment rod. Resection of the anterior and posterior aspects of the distal femoral condyles is accomplished through the use of another jig which has locking studs which are inserted into the fixation stud holes remaining in the femur after the femoral drill jig is removed.
A method for shaping the distal femoral surface employing the use of a relatively short femoral alignment rod which is positioned in the intramedullary canal is shown in a brochure entitled "New Jersey Tricompartmental Total Knee Replacement Surgical Procedure by Frederick F. Buechel, M.D.", 13 pages, issue date 1/1981, Form. No. 1280-32, from DePuy Division, Boehringer Mannheim Corporation, Warsaw, Ind. 46580.
In both of the above procedures, the alignment rods employed may not enable a surgeon to accurately follow the central long axis of the femur because the femur is not exposed to visual observation along its length. This can especially become a problem when the femur possesses a deformity which may somewhat alter its true central long axis.